Yuu Yuu Hakusho: loosely translates as Poltergeist Report. It is both an anime and a manga (comic book series). I've only actually seen one of the movies, and I've only read a couple of the manga, so I am not by any stretch of the imagination an expert on this series. I just like it.
Yusuke: As near as I can figure out the story is about Yusuke , a teenager in Japan who screws up his own death by doing a good deed at a most inauspicious moment. Because of the good deed the God of the Dead, Koenma, (very strange character--has both an adult and a child form that he switches back and forth between) can't send him where he intended to send him. Koenma has no choice but to bring him back to life. Of course there is a catch. Yusuke must work for Koenma as one of his spirit detectives. He has to track down rogue demons and capture or destroy them.
Kuwabara: Working with Yusuke is the rest of his team. First, a human named Kuwabara . He's physical very strong---but doesn't really strike me as the sharpest tool in the shed. He's madly (and I do mean madly---he goes positively nuts over her) in love with Yukina. (More on her later).
Kurama: Then there is Kurama . Kurama is in actually a Youko--a Fox Spirit, also called a Kitsune. He's many hundred years old---spent most of his life as a thief. Hunters injured him one day and he fled into the human world to hide. He ended up hiding in the unborn body of Shuuichi Minamino. And to his surprised--got born again. So now he's a Fox Spirit, stuck in the body of a human teenager. His family and classmates only know him by his human guise. His team mates know his true nature. (He got stuck working for the Spirit Detectives when he stole a magical artifact in an effort save his human mother's life.) Curiously, he too shifts shape from time to time. His human form is an unusually beautiful red-haired teenage boy (some people argue that Shuuichi Minamino was supposed to be a girl---but Kurama changed his gender when he took over the human body). His Youko form is that of a 7 foot tall silvered haired fox creature, as seen below:
Hiei: Then there is Hiei. Hiei is a Fire Demon, who was born into a race of Ice Demons. Needless to say, he was kicked out of the clan. Tends to make him rather rude, ill mannered and hard to get along with. He also stole something he shouldn't have, and was condemned to become one of the Spirit Detectives as well (not really condemned---it's not that bad of a job---they all seem to have a lot of fun sometimes.)
Hiei is also the twin brother of Yukina (yes, she's an Ice Demon---also a really sweet Healer). Hiei knew he had a sister, but didn't know where to find her. So he had a Jagan (third eye) implanted in his forehead to help him track her down. Trouble was, there was a price to pay for getting the Jagan---he can't tell Yukina who he really is.(Some people argue that this has nothing to do with why Hiei won't tell Yukina who he is---he simply won't tell her because he doesn't think he's a worthy enough brother for her.) Kurama is the only one who knows that Hiei is Yukina's brother, but he's been sworn to secrecy. Needless to say, Hiei doesn't like Kuwabara much---Kuwabara keeps fawning over his sister, and Hiei is in no position to say anything about it.
In any event, all four of these young men (age is relative) work together to track down rogue demons for Koenma. They are called the Reikai-Tantei (Spirit World Detectives). All of them have various weapons at their disposal for fighting.
Yusuke uses something called the Rei-Gun (yes, it is a ray gun!!). Actually he's simply able to focus a powerful burst of spirit energy through his first finger, so that he can literally 'shoot' his enemies.
Kuwabara uses something called Rei-Ken (Spirit Sword). He can focus a beam of spirit energy into a sword like object to attack his enemies with.
Kurama: He appears to have pretty much unlimited control over plants (I know, doesn't sound very impressive--but when the plant is a hundred foot tall, man-eating Venus Fly Trap, monsters tend to turn rather green.) He's also able to shape shift into his Youko form---which seems to be much more powerful than his human form---stronger, faster, heals quicker. He also has something called the Rose Whip. He pulls a rose out of his hair---and no I don't know how it got there or how many he keeps on stock---and turns it into a rather large, deadly whip. He also occasionally uses roses or rose leafs as daggers. The guy REALLY likes roses.
Hiei: He's very strong, and very fast---VERY fast. Apparently he's fast enough to pretty much defy gravity, dodge bullets, run between raindrops--that sort of thing. He also has the Jagan (third eye) which aside from giving him psychic abilities, also gives him the power to control the minds of lesser creatures. He's an excellent swordsman--perhaps one of the best around. He appears to possess some power over the element of fire (probably comes from being a fire demon). And last but not least he has a weapon called Enstatsu Kokuryuuha--which I think translates as the Black Dragon Flame, or attack of the black dragon fire or something like that. It's a cool dragon tattoo on his arm that comes to life and pretty much destroys everything within a ten city block radius--give or take a few streets.
Last but not least---why I write about these characters and where the whole Yaoi concept comes in: (Yaoi--the Western term is Slash). Hiei and Kurama----they're just too cute together!! Yusuke has a full-time girlfriend named Kieko. Kuwabara is crazy about Yukina. But Kurama and Hiei just seem to spend waaaaay too much time together. Curiously, I've noticed that even though the main character of this series is supposed to be Yusuke, Kurama and Hiei seem to be the two favorites of fanfic writers.
Language: It seems to be customary in writing Yaoi fiction (or gen for that matter) to use a great deal of Japanese in the dialogue of the stories. Of course a lot of the people who read (and write) these stories speak only English. Nonetheless, after a few dozen of these tales even we Americans who think we can get by with only one language, start to pick up a smattering of Japanese words. I started out reading YYH stories, then discovered Gundam Wing, and a couple of other rather interesting mangas---and would have dearly loved to have a Japanese dictionary handy to figure out what everyone is saying. From what I can figure out a lot of the language is more colloquial in nature, and it's often difficult to find good translations in formal dictionaries.
In my writing, I try to make certain that any non-English term I use is referenced in someway so that the meaning is fairly obvious from the context......but that doesn't always work. So to help out---here's a few of the most common terms I've noticed popping up in various other tales.
Ai Shiteru: "I love you". Can't have a yaoi tale without this popping up from time to time. From what I understand this is actually a very formal way of saying this---and implies a certain degree of seriousness or commitment.
Arigatou: "Thank you". There are more formal ways of saying this as well.
Baka: "Idiot!" or "Stupid"
Bishounen: "beautiful boy". All the guys of anime seem to fit this description.
Chibi: "little"; You see this word a lot in reference to characters in manga---as near as I can figure it simple refers to the little cartoonish-looking version of the character that shows up typically in a humorous or silly scene of some sort.
Chikushou: "Damn it!" (look ma! I can curse in Japanese!) I've heard a bunch of different translations for this word---and I think it actually means something a bit stronger than just 'damn it', but I can't get anyone willing to confirm this.
Daijoubu Ka: "Are you alright?" And there are several variations on this them. Basically if you see 'daijoubu' in the phrase someone is either asking if someone else is alright, or admitting that he or she is alright. Alright?
Gomen; or Gomen Nasai: "I'm sorry" or "I'm very sorry"
Hai: "Yes"
Hn: Okay this isn't actually a word....but you'll still see it all the time in anime fiction. In Western fiction it would show up as 'hmmm', or as a 'harrumph' or a snort of disgust depending on the context.
Itooshi: "Beloved"
Ja ne: "See you later"--a very informal phrase
Kaasan: "mother"
Kawaii: "Cute" as in 'he looks very kawaii'
Kisama: "&*#(@&" (just kidding) I think it basically translates "Bastard". It's a derogatory way of addressing someone.
Kitsune: "fox"
Koibito: "lover". A common term for a boyfriend or a girlfriend.
Koorime: "Ice Maiden" This is a race of Ice Demons who are all supposed to be female. Yukina is a Koorime. Hiei is often referred to as a Koorime as well, though technically this is impossible since he's a fire demon and a male. I guess I can see why he was kicked out of his tribe....didn't quite fit in.
Kuso: "shit!" Not too dissimilar from kisama---often spelled without the 'u' as K'so.
Lemon: Yes, its an English word! Actually this just refers to the rating typically found on yaoi fiction. A Lemon rating means that it is sexual explicit, like a "NC17" rating. A Lime rating means its more like an "R" rated story. And a "Slightly Citrus" rating means it really only hints at sex.
Maikai: "Demon World" Where Hiei and Kurama initially come from.
Nani: "What?"
Ningen: "human"
Ningenkai: "Human world". Earth.
Oniisan: "brother"; (By the way, if you read a lot of YYH fiction you might get confused over the correct name of Kurama's little brother....most writers refer to him as "oniisan' just so it's clear that they are talking about Kurama's brother. Strange as it may seem Kurama's little brother is named "Shuuichi" which also happens to be Kurama's human name.....and no I don't know why this happened.)
Reikai: "Spirit World" Where souls go when their bodies die. Apparently there is a lot of paper work involved.
Shimatta: "Shit"; yet another cuss word (these are important! pay attention)
Shinigami: "God of Death" okay I only threw this in because I like Gundam Wing. Koenma or Enma seems to be the Death God in YYH.
Youkai: "Demons"---though Demons are not the typical hell, fire and brimstone type of demon we get in Western Mythology. See note below on Demons.
Youki: "Energy". This term and youkai are a bit confusing. Youkai refers to the actual creature. Youki refers to the energy the demon possesses.
Youko: "Spirit Fox". Not to be mistaken with Youkai---Youkai is a more generic term for the whole lot of these supernatural creatures. A Youko is specifically a fox type creature, just like a Koorime is a Ice Demon.
Note on Demons: The word Demon is used as a general term here to refer to any sort of Supernatural Entity. I think in the Western world we'd refer to these creatures as Fey or Faerie. Many of these demons or Youkai are evil---and look rather hideous. Many are evil, but look beautiful. And then there are some that are good in nature. They come in all shapes and sizes (and hair color apparently), of both the good and evil persuasion, and pretty much have the same sorts of difficulties with life that humans tend to. Even the gods in these stories have to suffer the agonies of paper work.